The present invention relates to a jack which has a tip contact piece for engagement with a tip electrode of a plug upon its insertion into the jack body.
FIG. 1 shows a conventional jack of this kind. When a plug 12 is not inserted, a tip contact piece 11 assumes such a position as indicated by the broken lines in FIG. 1A, whereas when the plug 12 is inserted, the tip contact piece 11 is thrust aside or displaced by a spherically-headed tip electrode 13 of the plug 12 as shown in FIG. 1B, and as the plug 12 is further pushed into the jack, an engaging protrusion 15 of the tip contact piece 11 slides down the spherical surface of a radial protrusion 14 of the tip electrode 13 into engagement with its neck 16 as depicted in FIG. 1A. As a result of this, the plug 12 is anchored to the jack and the tip end portion 17 of the tip contact piece 11 resiliently contacts the radial protrusion 14 of the tip electrode 13, thus establishing electrical connection between the tip contact piece 11 and the tip electrode 13.
To ensure good contact between the tip end portion 17 of the tip contact piece 11 and the radial protrusion 14 of the tip electrode 13, the prior art jack is designed so that the tip contact piece 11 extends close to or across the center axis X of the jack as indicated by the broken lines in FIG. 1A while not in use but is displaced relatively greatly when the plug is inserted in the jack. Accordingly, the amount of displacement D of the tip contact piece 11 is large between its initial position (indicated by the broken lines in FIG. 1A) and its outermost position where the engaging protrusion 15 makes contact with the radial protrusion 14 of the plug 12 as depicted in FIG. 1B. For example, in the case where a tip contact piece 11 of phosphor bronze, 0.4 mm thick, is used for a standard 6.4 mm diameter plug, it is customary in the prior art that the length L of the contact piece 11 is 11 mm and its maximum amount of displacement D is 3 mm or more, and the initial position of the engaging protrusion 15 of the tip contact piece 11 is close to the center axis X of the jack. That is, the engaging protrusion 15 projects into the plug insertion hole to a radial depth of about 50% of its inner diameter. Since the tip contact piece 11 is subjected to substantial displacement, a highly resilient material (phosphor bronze, usually) is used therefor so that the resiliency of the tip contact piece 11 will not be impaired by its displacement, and this inevitably raises the material cost. Moreover, the tip contact piece 11 is formed long with a view to maintain its resiliency, and hence is bulky, and this also increases the material cost.